1. Field of the Invention
This invention relates to an envelope folding machine, and more particularly, to an envelope folding machine for forming envelopes which includes a vacuum table with at least one belt moving across the vacuum table to hold and transport the envelope blank through a folder in the folding apparatus.
2. Description of the Prior Art
In automated envelope forming operations, it is well known to provide a folding machine which includes plowshare type folding mechanisms positioned on the folding machine for folding the envelope blanks along the longitudinal axis of movement of the blank while the blank is controlled and moved past the plowshares by means of rollers. The use of a vacuum to hold and transport envelope blanks in envelope making machines is also well known in the art.
U.S. Pat. No. 1,834,564 discloses a feeding apparatus for drawing blanks from a stack and folding the blanks by means of a roller with apertures connected to a vacuum source.
U.S. Pat. No. 2,037,561 discloses an endless conveyor belt with perforations for receiving instrumentalities wrapped in gauze with free ends of the gauze forming leading and trailing end flaps. A suction nozzle grasps the leading end flap and pulls it over the body of the instrumentality while a blower opposite the suction source blows the gauze upwardly to lift the leading end flap away from the conveyor and toward the suction nozzle. The mechanism is duplicated for acting on the opposite end flap and provision is made for a means to transfer the instrumentalities from one conveyor to another.
U.S. Pat. No. 2,754,113 discloses a sheet folding machine wherein the material to be folded is fed onto two parallel central conveyor belts which raise the material at the sides such that the center section of the material is conveyed beneath a plate. As the material passes beneath the plate it is clamped and the sides are folded over by cross plates. The article is thereafter passed over a cross folding roll above which is positioned an air blast pipe which is operated to send a blast of air against the material and force the material between rolls to provide a crossfold after which it is conveyed to a stacker.
U.S. Pat. No. 2,846,215 discloses a device utilizing rolls with vacuum apertures to grip and fold endless bands of paper.
U.S. Pat. No. 3,685,818 discloses a method for folding diapers on a collapsible suction plate with hinged sections corresponding to the folded portions of the articles to be folded. A pair of suction discharge rolls remove the diapers from the suction plate and transport them to a packaging carton.
U.S. Pat. No. 3,870,292 discloses the use of rolls with apertures connected to a vacuum source to transport and fold a continuous web of paper.
U.S. Pat. No. 4,682,977 discloses an apparatus for folding side flaps inwardly in a continuous web of material. The continuous web is cut by a die roll pair transversely to the longitudinal axis of the web. The web of material is held between a vacuum belt and a friction belt, and the flaps formed by the die roll pair are folded by friction belts at an angle to the longitudinal axis of the material to be folded.
U.S. Pat. No. 4,549,728 disclose a vacuum table having at least one row of apertures which is used to apply a vacuum to a sheet of paper as it approaches a head stop, to slow the paper before it reaches the head stop to prevent wrinkles and inaccurate folds. When the paper reaches the head stop, a chopper folder introduces the paper between two fold rollers turning in opposite directions to fold the paper.
Although the prior art discloses the use of a vacuum to grip and move either a sheet or web of material, as well as a vacuum for slowing the forward advancement of a sheet of material, there remains a need for a vacuum table used in conjunction with a plowshare type folding device to better perform the controlling function of the blank as it passes through the folder area and to simplify the construction of the envelope blank folding apparatus to enable the operator to more easily adjust and maintain the apparatus.